JPH07130724A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form an element isolating film in a simple step by exposing a silicon substrate to a plasma, forming an SiC damaged layer on this part, removing a mask and heat treating the substrate to form the isolating film at a predetermined region. CONSTITUTION:On a silicon substrate 1, a resist pattern 2 covering an element isolating film forming region is formed after a resist coating, mask exposure and development. This is used as a mask, and the surface of the substrate is exposed to a plasma, using a CF4-CHF3-Ar reactive gas, thereby forming an SiC damaged layer 3 is formed on the surface of the substrate. The pattern 2 is removed to expose an element isolating film forming region 4 on the substrate. The substrate is put in a heat treating furnace to pyro-oxidize this region 4, thereby forming an element isolating film (SiO2).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a technique for forming an element isolation film by a local oxidation method.

[0002]

2. Description of the Related Art Local Oxidation Method (LOCOS)
(ion of silicon) is an important basic technology for forming an element isolation film in the manufacturing technology of semiconductor elements. With the progress of LSI technology, high integration and miniaturization thereof have been advanced, and a technique for forming a fine element isolation film is also required.

In the conventional LOCOS, a method of thermally oxidizing a silicon nitride film (Si ₃ N ₄ ) as a mask was used to form an element isolation film on the silicon substrate. When formed on the silicon substrate and oxidized at a high temperature, crystal defects such as dislocations may occur in the silicon substrate. Therefore, before the silicon nitride film is deposited as a buffer layer, a thin thermal oxide film is formed to prevent defects.

However, in such a method, it is necessary to perform the work of removing the silicon nitride film after the formation of the element isolation film in a phosphoric acid solution kept at a high temperature for a long time, which takes a lot of time and labor. become. Therefore, a technique has been proposed in which a silicon carbide film (SiC) is used in place of the silicon nitride film, the silicon carbide film is directly deposited on a silicon substrate by a CVD method, and the silicon oxide film is used as a mask to perform thermal oxidation (for example, Japanese Patent Laid-Open No. Hei 10 (1999) -135242). 1-7641 (H01L21
/ 94)).

Also in this conventional example, after forming the element isolation region, Si is formed in order to form an element in the element formation region.
A step of once removing the C film is required, but this work is
It is somewhat easier than working in hot phosphoric acid as described above.

[0006]

In the conventional example, compared with the normal LOCOS method, an oxidation resistant mask, that is,
Although the work of removing the SiC film is somewhat easy, as described in Japanese Patent Application Laid-Open No. 1-7641, the SiC film is a chemically stable substance. This is difficult, and it is necessary to first remove the oxide film and then remove it. Therefore, there is a problem that the manufacturing cost is increased due to the labor and the material cost.

The present invention relates to a method of manufacturing a semiconductor device,
The purpose is to eliminate such problems.

[0008]

A method of manufacturing a semiconductor device according to the present invention comprises forming an element isolation film by oxidizing a silicon substrate by a local oxidation method, and forming the element isolation film on the silicon substrate. A step of forming a mask covering a predetermined area and plasma irradiation of the silicon substrate with a gas containing at least carbon are performed.
The steps of forming a C-damaged layer, the step of removing the mask, and the step of heat-treating the silicon substrate to form an element isolation film in the element isolation film formation planned region are performed.

[0009]

When the surface of the silicon substrate is plasma-irradiated with a gas containing carbon (C), a damaged layer is formed on the surface of the silicon substrate. That is, gas containing carbon (CHF
₃ , CF ₄ , CH ₂ F ₂ , C ₃ F ₈ , C ₂ F ₆ , CCl ₄ etc.), the surface of the silicon substrate becomes silicon carbide (SiC) due to carbon atoms generated during the irradiation. SiC damage occurs, and a SiC layer is formed.

Regarding the conversion of the silicon surface into SiC,
It is described in detail in Surface & Interface Anal., 9,275 (1986). When this SiC damage layer is formed on the surface of the silicon substrate, even if the silicon substrate is thermally oxidized, the growth of the oxide film at the damaged portion is significantly hindered. Therefore, in the present invention, by utilizing this characteristic, the SiC damage layer is used as an oxidation resistant mask in the local oxidation method.

Although the SiC damage layer hinders the growth of the oxide film, it does not mean that it does not grow at all, and the damage is gradually improved by the heat treatment during the local oxidation. Therefore, when the formation of the element isolation film is completed, the portion of the SiC damage layer remains as a thin oxide film, but this portion can be easily removed by performing wet etching with hydrofluoric acid. Therefore, the SiC damage layer does not remain in the element formation region.

[0012]

EXAMPLE FIG. 1 shows a process of forming an element isolation film in an example of the present invention. Step: A resist pattern 2 is formed on the silicon substrate 1 through operations such as resist coating, mask exposure, and development to cover the element isolation film formation planned region (FIG. 1A). Process: Using this resist pattern 2 as a mask, CF ₄
-CHF ₃ -Ar-based reactive gas (CF _4: 20sccm, CH
Plasma irradiation is performed on the surface of the silicon substrate 1 using F ₃ : 20 sccm and Ar: 400 sccm (FIG. 1B).
The conditions at this time are as follows: chamber pressure: 250 mTorr, RF
Output: 800 W, time: 2 minutes.

As a result, S is formed on the surface 1 of the silicon substrate.
The iC conversion damage layer 3 is formed. FIG. 2 shows XPS (X-ray excited photoelectron spectroscopy: C _{1 S} of the SiC damage layer 3).
X-ray Photoemission Spectroscopy) profile. Approximately 283 eV, which is evidence of Si-C bond
Since a peak is observed in the vicinity (point A in the figure), it can be seen that the SiC damage layer is formed.

FIG. 3 is a characteristic graph when the RF output is changed as a condition for forming the SiC damage layer 3. From this, it is understood that the carbon concentration becomes constant when the SiC damage layer reaches about 200 Å regardless of the RF output. Process: The resist pattern 2 is removed to expose the element isolation film formation scheduled region 4 on the silicon substrate 1 (FIG. 1).
C).

Process: The substrate 1 prepared in the process is put in a heat treatment furnace and subjected to Pyro oxidation (conditions, temperature:
1000 ° C., time: 130 minutes, H ₂ : 3SLM, O ₂ : 3
By performing the SLM, the element isolation film formation planned region 4 is oxidized and the element isolation film 5 (Si having a thickness of 5000 Å is formed).
O ₂ ) is formed. Since the SiC damage layer 3 is formed in a portion other than the element isolation film formation scheduled region 4, the formation of an oxide film is suppressed. However, as will be described later, this SiC damage layer 3
Is gradually improved by heat treatment, and when the formation of the element isolation film 5 is completed, a thin oxide film 6 (SiO 2
₂ ) is formed (300Å is formed under the above conditions).

The thin oxide film 6 (although the element molecular film 5 becomes slightly thin) can be removed by wet etching with hydrofluoric acid on the entire surface to easily form an active region. FIG. 4 is a graph showing the relationship between pyrooxidation time and oxide film thickness when the RF output is changed as a condition for forming the SiC damage layer 3.
If the SiC damage layer 3 is not formed (in the figure,
), The oxide film grows smoothly according to the oxidation time.

If the SiC damage layer 3 is formed, the damage layer is improved for a while (that is, Si--C).
It takes time to break the bond), and after the improvement, the oxide film gradually grows according to the reaction formula of SiC + 2O ₂ → SiO ₂ + CO ₂ . It can be seen from FIG. 4 that the lower the RF output, the faster the damage is improved and the formation of the oxide film begins. This indicates that the higher the RF output, the higher the degree of SiC damage. For example, the thin oxide film 6 has a thickness of 20.
When various conditions of thermal oxidation are set so as to be 0 Å, the element isolation film 5 is changed by changing the RF output.
The film thickness of can be changed. That is, as the RF output is higher, the formation of the thin oxide film 6 is delayed, and accordingly the element isolation film 5 is thicker.

[0018]

According to the method of manufacturing a semiconductor device of the present invention, an SiC damage layer is formed on the surface of a silicon substrate,
Since this is used as an anti-oxidation mask for the local oxidation method, the element isolation film can be easily formed without the trouble of forming the SiC layer and removing it after the local oxidation.

[Brief description of drawings]

FIG. 1 is a sectional view sequentially showing a manufacturing process of a semiconductor device according to a first embodiment of the invention.

FIG. 2 is a diagram showing an XPS profile of a SiC damage layer.

FIG. 3 is a diagram showing the relationship between the depth of a SiC damage layer and the carbon ion concentration.

FIG. 4 is a diagram showing the relationship between pyrooxidation time and element isolation film thickness.

[Explanation of symbols]

 1 Silicon substrate 2 Resist pattern (mask) 3 Damage layer made of SiC 4 Element isolation film formation planned region 5 Element isolation film

Claims (1)

[Claims] 1. A method for forming an element isolation film by oxidizing a silicon substrate by a local oxidation method, the method comprising: forming a mask on the silicon substrate to cover the area for forming the element isolation film; and the silicon substrate. Plasma irradiation with a gas containing at least carbon, and SiC
A semiconductor device comprising: a step of forming an oxidization damage layer; a step of removing the mask; and a step of heat-treating the silicon substrate to form an element isolation film in the element isolation film formation planned region. Manufacturing method.